Application of an objective method for localizing bilateral cortical FDG PET abnormalities to guide the resection of epileptic foci

Purpose: In order to improve the objective localization of bilateral cortical abnormalities in positron emission tomography (PET) image volumes, we developed a new three-dimensional image processing technique. The accuracy of this approach with respect to invasive subdural electroencephalography (EEG) data was assessed in a group of children with neocortical epilepsy. Methods: Glucose PET image volumes were obtained from 12 epileptic children (mean age 5.2±4.3 years). Bilateral cortical areas of abnormal glucose metabolism were objectively determined using two conditional criteria assessed against a normal database. The normal database was derived from a group of 15 adult controls (mean age 27.6 years). The spatial relationship between seizure onset electrodes and PET abnormalities was assessed using a conventional receiver operating characteristic (ROC) analysis as well as using a newly defined spatial proximity index (SPI), which characterizes the association between adjacent, but not coincident, abnormalities. Results: ROC analysis at the 2 standard deviation (SD) threshold, revealed an accuracy of 65% to detect seizure onset areas with a sensitivity of 64±17% and a specificity of 66±24%. Sensitivity decreased to 46±24% at the 3-SD threshold with a specificity of 80±21% (accuracy 75%). The average value for the SPI was determined as 3.82±1.65 which was 20% lower than the SPI value calculated using a simple in-plane two-dimensional asymmetry between homotopic cortical segments (4.52±3.82). Conclusion: The presented image processing technique improves localization of cortical abnormalities and provides valuable imaging clues for placement of subdural EEG grids prior to surgical resection.